LARGE SCALE, MONODISPERSED OCTAHEDRAL BiVO4 MICROCRYSTALS, PHOTOSTABILITY AND WATER OXIDATION THEREOF

Abstract

A method of preparing bismuth vanadate particles is described. The bismuth vanadate particles prepared via ultrasonication and hydrothermal treatment exhibit controlled morphology (e.g., octahedral shape) and crystallinity (e.g., tetragonal crystal symmetry). A photoelectrode containing bismuth vanadate particles and a method of using the photoelectrode in a photoelectrochemical cell for water splitting is also provided.

1 . A method of preparing bismuth vanadate particles, the method comprising:
 mixing a bismuth(III) salt and an acidic aqueous solution to form a bismuth mixture;   mixing a metavanadate salt and a basic aqueous solution to form a vanadate mixture;   mixing the vanadate mixture and the bismuth mixture to form a reaction mixture that is simultaneously subjected to ultrasonication; and   hydrothermally treating the reaction mixture thereby forming the bismuth vanadate particles,   wherein:   the bismuth vanadate particles have an octahedral shape; and   the bismuth vanadate particles comprise crystalline BiVO 4  having a tetragonal crystal symmetry.   
     
     
         2 . The method of  claim 1 , wherein the bismuth vanadate particles have an average particle size in a range of 0.8-6 μm. 
     
     
         3 . The method of  claim 1 , wherein the reaction mixture is subjected to ultrasonication at a frequency in a range of 17.5-22.5 kHz. 
     
     
         4 . The method of  claim 1 , wherein the reaction mixture is subjected to ultrasonication at an amplitude in a range of 8-35%. 
     
     
         5 . The method of  claim 4 , wherein the reaction mixture is subjected to ultrasonication at an amplitude in a range of 18-22%, and wherein the bismuth vanadate particles consist essentially of crystalline BiVO 4  having a tetragonal crystal symmetry. 
     
     
         6 . The method of  claim 1 , wherein the reaction mixture is hydrothermally treated at a temperature of 100-250° C. 
     
     
         7 . The method of  claim 1 , wherein the bismuth(III) salt is bismuth(III) nitrate. 
     
     
         8 . The method of  claim 1 , wherein the metavanadate salt is ammonium metavanadate. 
     
     
         9 . The method of  claim 1 , wherein the acidic aqueous solution comprises nitric acid, and the basic aqueous solution comprises sodium hydroxide. 
     
     
         10 . The method of  claim 1 , wherein the bismuth mixture further comprises an ionic surfactant. 
     
     
         11 . The method of  claim 10 , wherein the ionic surfactant is sodium dodecylbenzene sulfonate. 
     
     
         12 . A BiVO 4  photoelectrode, comprising:
 a conducting substrate; and   bismuth vanadate particles present on a surface of the conducting substrate,   wherein:   the bismuth vanadate particles have an octahedral shape; and   the bismuth vanadate particles comprise crystalline BiVO 4  having a tetragonal crystal symmetry.   
     
     
         13 . The BiVO 4  photoelectrode of  claim 12 , wherein the bismuth vanadate particles have an average particle size in a range of 0.8-6 μm. 
     
     
         14 . The BiVO 4  photoelectrode of  claim 12 , wherein the conducting substrate is fluorine-doped tin oxide. 
     
     
         15 . A photoelectrochemical cell, comprising:
 the BiVO 4  photoelectrode of  claim 12 ;   a counter electrode; and   an electrolyte solution comprising water and an inorganic salt in contact with both the BiVO 4  photoelectrode and the counter electrode.   
     
     
         16 . The photoelectrochemical cell of  claim 15 , wherein the electrolyte solution has an inorganic salt concentration of 0.05-1 M. 
     
     
         17 . The photoelectrochemical cell of  claim 15 , further comprising a reference electrode. 
     
     
         18 . The photoelectrochemical cell of  claim 15 , wherein the BiVO 4  photoelectrode has a photo-current density in a range of 0.15-1.2 mA/cm 2  when the photoelectrochemical cell is subjected to a bias potential of 0.5-1.3 V vs RHE under visible light irradiation. 
     
     
         19 . The photoelectrochemical cell of  claim 15 , wherein the BiVO 4  photoelectrode has a photo-to-current conversion efficiency (IPCE) in a range of 2-25% when the photoelectrochemical cell is subjected to a bias potential of 1.23 V vs RHE under visible light irradiation, and an applied bias photo-to-current efficiency (ABPE) in a range of 0.02-0.3% when the photoelectrochemical cell is subjected to a bias potential of 0.7-0.85 V vs RHE under visible light irradiation. 
     
     
         20 . A method of splitting water into H 2  and O 2 , the method comprising:
 subjecting the photoelectrochemical cell of  claim 15  to a bias potential of 0.5-2.0 V; and   concurrently irradiating the photoelectrochemical cell with visible light thereby forming H 2  and O 2 .